From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98878][MODERATE REGULAR] irqchip/gic-v5: Immediately exec priority drop following activate [ Upstream Date: Mon, 26 Oct 2026 23:02:42 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98878 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: c29bb5acd0cad0b49399d1399dd1bacb39e41438 List-Id: CVE: CVE-2026-98878 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: irqchip/gic-v5: Immediately exec priority drop following activate [ Upstream Commit: c29bb5acd0cad0b49399d1399dd1bacb39e41438 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c29bb5acd0cad0b49399d1399dd1bacb39e41438 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98878 Analysis date: Mon, 26 Oct 2026 23:02:42 -0400 ActionableScore: 3 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: Delayed GICv5 priority drop can let prolonged interrupt handling or guest execution starve other host interrupts, causing host-wide denial of service without a demonstrated memory-corruption or authorization primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98878 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98878 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: MODERATE REGULAR Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98878 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98878 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=1 LEGACY=MODERATE RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-754;CWE-691;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A logic error in the GICv5 interrupt lifecycle delayed the CDEOI priority drop until irq_eoi. Since all interrupts use the same priority, an active interrupt followed by a long running handler or direct guest entry could prevent every equal-priority interrupt from being signalled and cause host-wide denial of service. For the CVSS the PR:L value reflects that reliable adversarial triggering would normally require control of a local workload or guest with access to a forwarded physical interrupt. The issue is not directly network reachable and the diff provides no UAF, OOB access, information leak, or memory corruption primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4. The independent weaker Aegis shadow evaluated CVSS 4.7 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE DMAorINTERRUPT HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 2. * Conservative score: 3. Applied guest-to-host host-wide DoS safety calibration: 2 -> 3. * Raw paranoid score: 2. * Paranoid score: 3. No additional speculative primitive awarded. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +1 Reliable strong DoS: delaying CDEOI until `irq_eoi()` can prevent all equal-priority interrupts from being signalled during prolonged handling or guest execution. * +1 Cross-boundary host interference: the supplied evidence grounds a VM/direct-guest-entry path capable of suppressing host interrupt delivery, not merely a device-local stall. * Floor to 3: a grounded guest-associated host-wide interrupt-starvation effect should not remain in the ordinary 0–2 bucket. * No memory corruption, UAF, OOB access, authorization bypass, protected-resource access, confidentiality impact, or integrity primitive is shown. * No extra availability point: host interrupt starvation is the same DoS already counted. * No local-unprivileged bonus: access to the necessary forwarded physical interrupt and the complete attacker-controlled trigger are not established. * NEW52 B5-R, NEW53 B3-PENDING, and NEW54 B4-PENDING do not apply. 3. Reachability analysis The patch supports occurrence while injecting a physical interrupt into a guest and then entering or running that guest for an extended period. The hints identify a local workload or guest with access to a forwarded physical interrupt, but do not establish who provisions that interrupt, whether a guest alone can reliably force the complete sequence, or whether prior host-administrator setup is mandatory. There is no namespace-capability path, network reachability, race requirement, or memory-corruption prerequisite shown. Effective host-admin and UID-0 requirements therefore remain unknown. 4. Primitive and severity reading The primitive is interrupt lifecycle misordering: priority remains dropped too late, allowing one active interrupt to block delivery of all same-priority interrupts. This is CLASS_C availability behavior, not active structured-state corruption. The shown effect is potentially host-wide interrupt starvation; panic, persistent corruption, guest escape, and privilege escalation are unproven. ImportantCandidate is NO because no reusable corruption or security-boundary bypass primitive exists. Auto-downgrade remains allowed, although manual validation of guest-only triggerability and host impact is recommended. 5. One-sentence report phrase Delayed GICv5 priority drop can let prolonged interrupt handling or guest execution starve other host interrupts, causing host-wide denial of service without a demonstrated memory-corruption or authorization primitive. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether an untrusted guest can independently drive the full forwarded-interrupt sequence and reliably starve host interrupts without additional privileged VMM action. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: irqchip/gic-v5: Immediately exec priority drop following activate [ Upstream Commit: c29bb5acd0cad0b49399d1399dd1bacb39e41438 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c29bb5acd0cad0b49399d1399dd1bacb39e41438 Changed files: drivers/irqchip/irq-gic-v5.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c29bb5acd0cad0b49399d1399dd1bacb39e41438 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98878 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98878 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: unknown Paranoid ActionableScore: 3 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: MODERATE KPANIC detected for this report: NO Published priority for this report (same as in Subject): MODERATE REGULAR These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).